(Received April 25, 1988; accepted for publication July 23, 1988)
In order to measure the saturated absorption spectral width of methane, a high-resolution laser spectrometer was developed by means of a phaselock technique. The accuracy of the offset frequency and the frequency fluctuation was estimated to be about 22 Hz and 35τ-1Hz, respectively. In addition, an integral and a proportional-derivative(I-PD) control method was applied to the frequency scanning laser system and its response time was improved in comparison with an integral-proportional (IP) control method. The saturated absorption spectral broadening was measured as a function of laser output power P in µW and methane pressure p in mTorr. The spectral width of the saturated absorption of methane was expressed by
Γ(p,P) = 150.36 + 15.60 · p + 1.625 · P [kHz].Furthermore, its residual spectral width was analyzed for the geometrical and transit time broadening, and the saturation broadening and wave front effect were also discussed.